Immunochemistry of scorpion toxins. Immunogenicity of peptide 19-28 a model of an accessible and relatively rigid region

Serotherapy against Voltage-Gated Sodium Channel-Targeting αToxins from Androctonus Scorpion Venom

Because of their venom lethality towards mammals, scorpions of the Androctonus genus are considered a critical threat to human health in North Africa. Several decades of exploration have led to a comprehensive inventory of their venom components at chemical, pharmacological, and immunological levels. Typically, these venoms contain selective and high affinity ligands for the voltage-gated sodium (Na_v) and potassium (K_v) channels that dictate cellular excitability. In the well-studied Androctonus australis and Androctonus mauretanicus venoms, almost all the lethality in mammals is due to the so-called α-toxins. These peptides commonly delay the fast inactivation process of Na_v channels, which leads to increased sodium entry and a subsequent cell membrane depolarization. Markedly, their neutralization by specific antisera has been shown to completely inhibit the venom’s lethal activity, because they are not only the most abundant venom peptide but also the most fatal. However, the structural and antigenic polymorphisms in the α-toxin family pose challenges to the design of efficient serotherapies. In this review, we discuss past and present accomplishments to improve serotherapy against Androctonus scorpion stings.

[Management of scorpion sting in Morocco]

Scorpion stings are the first cause of poisoning, and represent between 30 and 50% of all cases reported to the Moroccan Poison Control Centre. Concerned by the size of the problem, we have paid special attention to this pathology. Through retrospective and prospective studies, it has been possible to determine the nature and the chronology of clinical stages, as well as the epidemiological, clinical and therapeutic factors of gravity. On this basis, we worked out a new management to provide support for patients. This management will standardize support provided at the national level, and will reduce the number of lethal case and rationalize spending by reviewing medication, transfer of patients and hospital care. This standardization is an essential component of the national strategy against scorpion poisoning. Other components include training of medical staff, awareness campaigns, and information systems to monitor lethal cases. A survey over five years shows a reduction in the number of lethal cases and rationalization of costs. Medical care provided rests upon the distinction between patients stung by scorpions and patients actually poisoned. The first category of patients will be monitored up to four hours after the scorpion sting, while poisoned patients will be transferred to an intensive care unit.

The use of polyacrylamide-based peptide synthesis resins for the generation of antipeptide antibodies

Antibodies directed against specific amino acid sequences can serve as probes for the protein molecules from which the sequence was derived, as well as affinity purification reagents. One of the major uses of synthetic peptides is for the production of such antibodies. Typically, antigens for this purpose are prepared by coupling the peptide to a macromolecular carrier such as bovine serum albumin or keyhole limpet hemocyanin. The steps for this process are peptide synthesis, peptide purification or desalting, coupling to the carrier protein, and purifying the peptide-protein conjugate. Techniques have emerged in which the amino acid sequence of interest is synthesized on a solid support using a noncleavable linkage and the resulting peptidyl-resin is injected into animals to elicit the antipeptide immune response. These procedures reduce the number of steps required to prepare the peptidyl-antigen. Water-compatible resins based on polyacrylamide have been utilized for this purpose. In this paper the composition of these supports and their use in the generation of antipeptide antibodies is reviewed.

Fine molecular analysis of the antigenicity of the Androctonus australis hector scorpion neurotoxin II: a new antigenic epitope disclosed by the Pepscan method

A set of 58 overlapping rod-bound peptides was used to map the antigenic reactivity pattern of a 64-residue neurotoxin (AaH II) from the venom of the scorpion Androctonus australis hector. Five anti-toxin rabbit antisera were assayed serially for their capacity to bind to each peptide in the set. Six regions of antigenic reactivity were thus identified (sequences: 1-8, 4-12, 27-35, 39-45, 52-58 and 55-61). When positioned on a 3-D model of the toxin, these regions appeared to correspond to either beta-turn or extended parts of the molecule. The antigenic regions revealed by this technique agree fairly well with those previously mapped on the same toxin by different methods. One discrepancy was, however, that the present study shows the N-terminus to be strongly reactive with anti-toxin antibodies. The antigenicity of this region was confirmed, since rabbit antibodies raised against a synthetic peptide mimicking the sequence 1-8 of the toxin were found to bind the toxin with high efficiency. A fine analysis of the recognition of this region was performed. Alanine-containing analogs of the sequence 1-7 and peptides mimicking the N-terminal of the four main toxins of AaH were probed with anti-toxin and anti-peptide antibodies. Lysine 2, aspartic acid 3 and glycine 4 were shown to be key residues in the recognition of the N-terminal region of the AaH II toxin by anti-toxin antibodies. In contrast, a loose specificity of recognition was shown by one anti-peptide serum which was, in addition, able to recognize the N-termini of all four AaH toxins.

Identification of the epitope of a monoclonal antibody which binds to several cytochromes P450 in the CYP1A subfamily

The monoclonal antibody, 3/4/2, which was raised against purified rat cytochrome P450 isoenzyme 1A1 (CYP1A1) binds to cytochromes P4501A in many species. It was shown by immunoblotting that the antibody binds to CYP1A1 in microsomal fractions prepared from rat, mouse, rabbit, hamster and human. The antibody also binds to cytochrome P450 isoenzyme 1A2 in microsomal fractions prepared from rabbit and human, but not rat or mouse. Using purified isoenzymes in an enzyme-linked immunosorbent assay it was found that the affinity of binding to the two rabbit hydrocarbon-inducible isoenzymes is reduced compared with that for rat CYP1A1. Binding is not affected by denaturation of the antigens. The effects of chemical and enzymatic treatments on rat CYP1A1 showed that the epitope contains a trypsin-sensitive site that includes arginine, but lacks lysine. The epitope does not contain methionine, cysteine, aspartic acid or glutamic acid residues. In addition, digestion of the protein with cyanogen bromide produces a fragment of Mr 20,000 which contains the antibody binding site. By comparing the cross-reactivity of the antibody with the primary structures of CYP1A1 and 1A2 from the rat, mouse, rabbit and human, and by considering the results of the chemical and enzymatic treatments, it was possible to deduce the likely location and structure of the binding site of 3/4/2 on members of the CYP1A subfamily. It is concluded that the epitope for this antibody is Phe-Arg-His-Ser-Ser-Phe, which lies at positions 380-385 in rat CYP1A1. Further, it is predicted from a model of the tertiary structure of eukaryotic cytochrome P450 that a part of this binding site lies within a helix in the native protein.

Peptide component vaccine engineering: targeting the AIDS virus

Most of the successful vaccines developed to date induce protective immunity resembling that produced by natural infection. HIV infection does not induce protective immunity. Thus, previously successful approaches based on live- or killed-virus preparations may not yield an effective and safe AIDS vaccine and many feel that a more highly engineered vaccine will be required. Synthetic peptides represent extremely powerful tools for vaccine research and construct optimization. The theory and practice of vaccine engineering using synthetic peptide components is reviewed with special emphasis on progress towards development of a vaccine for AIDS.

The antigenic structure of a scorpion toxin

Scorpion toxins constitute a family of homologous proteins that exert potent pharmacological effects on ion channels. These proteins are immunogenic and constitute a good model for investigation of the molecular basis of antigenicity. In the first part of this article we summarize the results we have obtained in recent years concerning the location of the main antigenic regions of a model toxin, toxin II of the North African scorpion Androctonus australis Hector. Then, thanks to the recently available atomic coordinates of this toxin, we analyzed the relationships between the structural features of the protein and the location of the antigenic regions: we found that antigenic regions are located at exposed parts of the molecular surface, i.e. in reverse turns and the alpha-helix. These surface parts also correspond to segments of the polypeptide chain which are most accessible to a large spherical probe modelizing an antibody molecule. Finally, we obtained a general idea of what could be the main discontinuous antigenic determinants by looking for the neighboring relationships between the most exposed residues of the protein.

Direct immunization with synthetic peptidyl-polyamide resin. Comparison with antibody production from free peptide and conjugates with carrier proteins

An 11-amino acid residue peptidyl-linkage agent-polyamide resin complex was synthesized by the fluorenylmethyloxycarbonyl (Fmoc)-polyamide solid-phase system. Mice were immunized with the free peptide, peptidyl-resin and peptide coupled to the carrier proteins ovalbumin (Ova) and keyhole limpet haemocyanin (KLH). The immunogenicity of these materials was assessed by measurement of the capacity of the various antisera to bind the peptide in an enzyme-linked immunosorbent assay (ELISA). The peptidyl-resin exhibited enhanced immunogenicity compared to the free peptide. It is suggested that the time needed for screening for immunogenicity of large numbers of synthetic peptides thus be greatly shortened by using peptidyl-resins for immunization. This method eliminates laborious cleavage of peptide from resin, purification, coupling to carrier and the difficulties of handling peptides of low solubility.

Preparation and characterization of monoclonal antibodies against beta-bungarotoxin and its A- and B-chains

Splenocytes from Balb/c mice immunized with beta-bungarotoxin, a protein neurotoxin that exhibits phospholipase A2 activity, were fused with SP2/0 murine myeloma cells. Eighty-seven stable hybridoma cell lines were established which secrete monoclonal antibodies of the subclass IgG1 and K light chain and react with intact neurotoxin. Some antibodies were further analyzed. These recognize at least two immuno-dominant regions located on the A- and B-chains of the toxin, and the native toxin but show no crossreactivity with a protein homologous to chain A (porcine pancreas phospholipase A2) nor to chain B (toxin 1 from Dendroaspis polylepis). Two monoclonal antibodies inhibit phospholipase A2 activity of the neurotoxin but only one partially neutralizes its biological activity when injected together with the toxin, delaying the time of death.